Pressure container



Nov. 9,' 1943- .1. o. JACKSON PRESSURE CONTAINER Filed Aug. 6, 1941 3Sheets-Sheet l law llll

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PRESSURE CONTAINER Filed Aug. 6, 1941 3 Sheets-Sheet 2 1 T 1 I T /6 37PPPPPPPPPPPPTZP 37 P P v P p PF 35 39 39 5 INVENTO W (o, W W ww m 344;ATTORNEYS Nov. 9, 1943. J. o. JACKSON 2,333,792

PRESSURE CONTAINER Filed Aug. 6, 1941 3 Sheets-Sheet 3 INEKID NTOR BY 2ATTORNEYS Patented Nov. 9, 1943 PRESSURE CONTAINER James 0. Jackson,Grafton, Pa., assignor to Pittsburgh-Des Moines Company, a corporationof Pennsylvania Application August 6, 1941, Serial No. 405,647

11 Claims.

This invention relates to containers and particularly to closedcontainers or tanks of the type suitable for storing liquids underpressure, such pressure being usually caused or created by the vaporpressure of the liquid being stored.

Such containers have in the past been built in a variety of forms suchas spherical tanks which are especially suitable for moderately highpressures but which are quite costly to construct. Spheroidal tanks havealso been built and may be very efliciently designed for the conditionof a full tank with vapor pressure but which require considerablereinforcement or strengthening to withstand conditions of partialfilling. Relatively small pressure tanks have also been built with acylindrical shell and with dished heads or ends but such containers havebeen limited to the smaller sizes.

The customary large storage tank with a flat, conical or even adome-shaped roof is very limited in its ability to withstand internalpressure. The usual type of tank is only able to withstand a few ouncesof internal pressure per square inch. The vapor pressure of many liquidscommonly stored in large quantities such as gasoline frequently rangesfrom 2 to 15 pounds per square inch at a temperature of 100 F. Thisconventional type of large storage tank must, therefore, be vented toprevent such excessive internal pressure but venting results in loss ofvapors and, consequently, great economic waste.

An object of this invention is to provide a storage tank which throughits novel design and construction will safely withstand an appreciableinternal vapor pressure and which at the same time may be constructed ata cost only slightly in excess of the common type of large storage tank.

Another object of my invention is to provide a container which willwithstand an appreciable vacuum in the interior of the tank which mightbe caused from the condensation of vapors as the tank cools, forinstance, during the night. 4 Other and further objects and advantagesof my invention reside in the various combinations, subcombinations anddetails hereinafter described and claimed and in such other and furthermatters as will be understood by those skilled in this art or pointedout hereinafter.

In the accompanying drawings, in which like numerals designatecorresponding parts through out the various views:

Fig. 1 is a side elevational view, with parts broken away to reveal theunderlying structure, of a preferred embodiment of pressure tankresponding to my present invention;

Fig. 2 is a half plan of the tank of Fig. 1 with parts broken away toreveal the underlying structure, Fig. 2 being taken on the plane of line11-11 of Fig. 1 in the direction of the arrows thereof;

Fig. 3 is a fragmentary section showing a corner construction of my newtank;

Figs. 4 to 6, inclusive, are more or less diagrammatic viewsillustrating stress characteristics involved in my new tank; and

Fig. 7 is a side elevational view of a modified form of tank.

In fabricating a tank it is usually neither necessary nor practicable tobuild the same to withstand either the largest possible positiveinternal vapor pressure or the largest possible intemal vacuum which mayoccur during extremes of temperature variations to which the tank may besubjected. It is generally more economical and. better design practiceto construct the tank in such manner that a slight amount of vapor islost or wasted under the extreme conditions of pressure and vacuum abovenoted since to do otherwise would require a considerable increase in thecost of the container. In this connection I wish to point out that thetank of my present invention is capable of withstanding both theextremepressures and the extreme vacuums which may be encountered innormal usage of a tank of the present character. The accomplishment ofthe same is carried out by me without unduly complicating theconstruction of the tank and without objectionably adding to its cost.

Referring to Figs. 1 to 3, inclusive, it will be observed that my newtank is provided with an upright central cylindrical portion ill, adished sheet-metal bottom II and an oppositely dished sheet-metal top orroof l2. Members II and I2 have the form of a section of a sphericalsurface and, as will hereinafter be more fully apparent, are constructedon a large radius. The cylindrical portion I0 is provided on its upperedge with an annular upstanding band-like connecting member I! which isfirmly secured to member III as by welding 32. The center lines ofmembers l0 and H are in alignment but member I! is of a heavier orthicker section as will be apparent. A bar-like horizontal ring I4 ismounted on the upper edge of member I! in the position shown best inFig. 3 and the two members are securely united at right angles to oneanother as by means of the welds 3i.

An annular connecting member l8, which is frusto-conical in character,is secured, as shown, to member l4 as by means of welding 30. Member I8is positioned so as to intersect member l4 at or adjacent the upper edgethereof and so that its center line will, when'projected, pass throughthe center of symmetry of member [4, an intersection at this pointoccurring with the vertical center lines through members Ill and II, aswill be clearly apparent from Fig. 3. The

A short bar-like member is firmly secured as by welds 33 in the interiorangle formed between members I! and It. The radially outer end of aradial beam [9 is secured to member 20. As shown in Fig. 3, this isaccomplished both by means of bolts 94 passing through the said membersand also by the *welds 35 and 36. This provides a strong constructionwhich is simply and readily produced without objectiona'bly adding tothe expense of the tank and it is to be understood that members l9 and29 are preferably preunited at the plant or factory prior to shipment ordelivery. It will be understood that a plurality of members 20 isdisposed around the tank and that one such member is provided for eachradial beam i9, a typical spacing and relationship being illustrated inFig. 2. The number and size of radial beams depends, of course, upon theparticular tank and its intended service.

The radially inner ends of beams i9 are secured, preferably by welding,to the outer surface of the web of the annular channel Zia which has aU-shaped cross-section and a relatively small diameter, as shown. It isto be understood that a satisfactory connection between beams iii andmember 28a may also be made by bolts or in other suitable fashion. Asheet metal disc-shaped member 2! is welded or bolted to member Ziainteriorly thereof, 1. e. on the opposite surface of the web from beamsi 9. From the underside of disc 2| a column depends. The upper end ofcolumn 25 is suitably secured to the underside of said disc 2| and thisassembly forms a support for the inner ends of the beams i9.

The construction of the bottom portion of the tank is identical withthat already described in connection with the top. In other words,cylindrical portion III of the tank rests upon member l6 correspondingto the member I! above described and is secured thereto as by welding.Member it rests upon a horizontal member l3 corresponding to member Italready described and it is to be understood thatthe relationship ofmembers l6 and I3 is obtained and maintained in the manner described inconnection with Fig. 3. Similarly, members 23 are provided correspondingto the members 29 previously described. To each member 23 a radial beam22 is secured in a manner which will now be understood. The inner endsof the beams are secured to a structure which includes the disc 24 towhich the lower end of column 25 is secured and the circular channel24a, the construction and arrangement being the same as that alreadydescribed in connection with members 2| and 2m. Member Hi responds toand is similarly formed and mounted as member i8 already referred to.

Depending upon circumstances, the size of the tank and the load whichthe same must withstand, I may provide additional columns, designated as26, which are arranged in ring formation and which extend verticallybetween the radial beams I9 and 22. Circular girder-like members l9a andl9b may also be provided intermediate the center and periphery of thetank and these members are disposed upon the beams l9, which are ofchannel-shaped section as is apparent from Fig. 1. Similarly,girder-like members 22a and 22b are provided between beams 22 and thebottom ii of the tank. The circular girders 19a, 19b, 22a and 221; maybe suitably secured to the radial beams as by welding or bolting. y

In Fig. 4 I have illustrated a section through the tank roof i2 and thecontig ugus connecting member l8 apart from the balance of the tankstructure in order to illustrate the effect of internal pressure(indicated by the arrows marked P) acting upon the concave side of theroof l2. As there shown the exteriorly acting force 31 necessary toproduce equilibrium can be resolved into an outwardly acting horizontalcomponent 38 and a downwardly acting vertical component 99.

The forces acting on member I4 are indicated on the cross-section ofthat member illustrated in Fig. 5. As there shown, force 31 iscounteracted by forces 38, 39 and 40. Force 38 arises from the ringcompression of ring member ll in a horizontal direction. Forces 40represent the stress of members I9 through connecting member 20.Downwardly acting force 39 represents the vertical tensional forcebetween member i4 and member i'l caused by the internal pressure.

In Fig. 7, the modified form of tank there shown is provided with acentral portion 10' which has a surface generated by the revolution of acurve around the central axis of the tank. Otherwise, this form of tankmay be identical with or similar to that of Figs. 1 to 3, inelusive, Theparticular virtue of the tank of Fig. 7 is that the thickness of memberID may be less than that of member ID without sacrifice of strength or,for the same thickness, member 19 has appreciably greater strength thanID. This form of tank is,.however, best employed for tanks of very largediameter.

An important feature of my invention resides in the corner structure ofFig. 3 wherein member l4 cooperates with members l9 in permitting me toform the sheet metal top l2 as a spherical section of relatively largeradius. For example, in a tank 40 feet in diameter I find it iseconomical for the storage of gasoline with a vapor pressure of 10pounds per square inch to form a roof l2 of sheet steel to a sphericalsurface having a radius of approximately 66 feet, which requires, forthe unit stresses I prefer to use, a thickness of approximately 1; inch.Member I2 is, therefore, quite flat and intersects the cylindrical shelll0 and I! at an angle only a little greater than It is known that a,spherical shell subjected to internal pressure is stressed in tension,which tension is equal in all directions in a plane tangent to the shellat any point. In the case of a segment of a spherical shell thetensional stress in the shell is numerically equal to the internalpressure expressed in pounds per square inch multiplied by the radius ofcurvature expressed in inches and divided by two. In order that thesegment of the spherical shell be in equilibrium it is obviouslynecessary to apply a force around its extreme circumference, such as 31in Fig. 4, equal to the internal stress in the shell. This force beinginclined at a slight angle with the horizontal may readily be resolvedinto a horizontal and vertical component 38 and 39, respec- Force 33which is the horizontal component of force 31 imposes upon thecontinuous circular ring M a radial inward force completely around itscircumference as shown in Fig. 6 which for horizontal equilibrium mustbe balanced by two forces ll which must necessarily be equal fromconsiderations of symmetry. Forces 33, therefore, cause a ringcompression in member II and if force 38 is expressed in pounds perlineal inch of circumference, force ll is numerically equal to force 38times the radius to the center line of members l4. The total compressionin the ring M for tanks of usual sizes is considerable and would requirea section of considerable crosssectional area. I have found that theweight and cost of ring I! may be considerably reduced by the use ofbeam-like members l9 so connected that they assist in opposing theinward force 31, illustrated in Fig. 5, caused by the tension in topmember I2. I have found that theoretically if all of the inward force 31could be resisted by radial members IS the total theoretical weight ofsuch members would be exactly one-half of the total weight of member llif no radial member H! were used. However, from practical considerationsit is not desirable to assume the entire inward load 31 by members IQfor the reason that it becomes expensive to develop the inwardcompressive load through member 2| if an excessive number of members l9are used, for due to the relatively small circumference of members 2|and the fact that members l9 are converging toward the center of thetank it becomes increasingly difilcult to develop the compressiveresistance to force 31 across successive diameters of the tank where itis equalized and cancelled by forces 31 acting in the opposite directionon the opposite side of the tank. I have found, however, that a minimumcost for tanks of usual sizes is obtained if members l9 are designed soas to resist from about A to about /3 of the total value of forces 31.

Another feature of my design, and one which also determines to someextent the angular spacing of members 13, is the fact that these membersalso act to resist the forces tending to collapse the roof either fromexternal pressure or the weight of the roof itself or such loads as arecaused by wind or snow acting upon it. Since the roof I2 is relativelythin and has a relatively large radius it would not have very muchresistance against external pressure or loads. Members l9 are connectedat their inner ends to column-like member 25 through members 2| and 2 laand are connected on their outer ends to the tank shell I throughconnecting members 20. Curved rings I90 and I9!) are constructed so asto fit the curvature of the inside of roof l2 and are spaced so as toproperly support roof l2 and to assume from it any external loads orpressures without permitting undue distortion. The disposition of ringsl3a and l9b is such that the distortion of roof l2 caused by externalpressure is in the form of a series of concentric waves which greatlyincrease th resistance of the roof l2 to external pressure and whicheffectively transfers such pressure through members l9a and I3b to thebeam-like members I9 and thereby to the foundation through the tankshell l0 and the column member 25 OILif a similar pressure issimultaneously being exerted on the tank bottom member II the pressuresfrom members II and members l2 act against each other through mem- 10bers l0 and 25 and are counterbalanced.

In tanks of larger diameter it is desirable to use one or moreconcentric rings of intermediate column members 26 to shorten the spanof members l9 and 22. In such cases it is sometimes advantageous toprovide lateral or radial bracing for additional members 26 to increasetheir column effectiveness and shorten their slendemess ratio. Suchmodifications are deemed to form a definite part of this invention.

The roof l2 and the bottom II are not attached to any of the interiorsupporting members but are left free to expand with increasing internalpressure without causing high concentrations of stress on the internalsupporting framework or upon the members I I and I2 themselves.

Fig. 6 is a loading diagram showing in plan one-half of ring member l4loaded with radial loads 38 on the inside. In proportioning the size ofmember I4 I consider these radial loads 38 to act on member I 4 at itscentroid, such loads causing a ring compression and the totalcompressive force acting on the cross-section of member l4 being themagnitude of the inward forces 38 expressed, for example, in pounds perlineal inch along the centroid of member l4 multiplied by the radius ofthe centroid of member l4 also expressed in inches. This product is thetotal compressive force in the member and I usually deter- 40 mine thecross-sectional area on the basis of an allowable compressive fiberstress of about 25,000

pounds per square inch. Since the thickness and the width of member l4may be varied, a particular thickness and width may be found which willprovide the desired cross-sectional area and which will also permit theproper intersection of forces 31 and 40 at the centroid of member l4.

In actual practice I have constructed a 20 foot pressure container toscale which was designed in the manner hereindescribed for an internalpressure of five pounds per square inch. The container was filled withwater and tested by admitting water under pressure to the interiorthereof, the pressure on the interior being indicated by means of apressure gauge on the roof communicating with the tank interior. Straingauge readings taken during the progress of the test corroborate theabove rather closely and at a pressure of 7 /2 pounds per sqare inch,which represented a stress about equal to the yield point of the steelin member l3, strain gauge readings indicated that yielding was takingplace and mill scale began cracking off. The internal pressure wasincreased until finally at a pressure of 42 7 pounds per square inchseveral breaks occurred in member l0 causing a suflicient loss of waterto prevent a further increase of pressure. At the conclusion of the testit was found that member l4 had decreased approximately 5 /2 inches incircumference and member l3 had decreased 6% inches in circumference,indicating the extent of the yielding and also clearly demonstratingthat no elastic instability exists in member H! but that it has a largeexcess strength when designed in 75 the manner I have described.

I have described the form of my invention which I consider the mostsuitable for tanks of common-sizes and pressures but it is to beunderstood that the same is illustrative, not limitative. Other andfurther additions, omissions, substitutions and variations may beresorted to and all such are deemed to form a part hereof. Rather theinvention is that defined by the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A tank for the storage of large quantities of liquid having asubstantial vapor pressure at the temperature of storage and undergoingconsiderable variations in pressure in response to changing atmosphericconditions, which comprises an upright relatively thin cylindricalshell, a, thicker annular band-like connecting member of rectangularsection welded in position on the upper and lower edges of said shellwith the center line of each in alignment with the center line of saidshell, a bar-like ring member welded to the distal end of each of saidband-like connecting members and extending at right angles thereto, anannular connecting member of frusto-conical configuration welded, to theinner edge of each bar-like ring member and in such relationship theretothat the projection of the exterior surface of each annular connectingmember passes through the center of symmetry of the adjacent bar-likering member, and an outwardly convexed member ofsphericfal sectionwelded in position within each of said annular frusto-conical connectingmelnbers and forming a substantially uninterrupted extension thereof.

2. A tank of the construction set forth in claim 1 in which an axialcolumnar support extends vertically between said outwardly convexedmembers which intersect said shell at an angle only slightly in excessof 90 and in which radial bracing members extend in a substantiallyhorizontal plane between said band-like connecting members and saidcolumnar support.

3. A tank of the construction set forth in claim 1 in which eachband-like connecting member is provided with a plurality ofcircumferentially spaced inwardly projecting radial bar-like connectingmembers disposed in the interior angle between each of said band-likeconnecting members and its contiguous bar-like ring adapted to beconnected to the outer ends of radial bracing members extending betweensaid band-like connecting members and the central portion of said tank.

4. A tank of the construction set forth in claim 1 in which means isprovided for preventing movement of said band-like connecting members inresponse to changing pressure conditions internally and externally ofsaid tank and in which means is also provided for supporting said roofand bottom in predetermined spaced relationship in such manner as toprevent deformaticn due to changing pressure conditions, said meanstogether including an axial column terminating at each end in a cap-likedisk, an annular channel surrounding each such disk and to which suchdisk is secured, a plurality of spaced bar-like connections extendingradially inward from each of said band-like connecting members andsecured thereto and radial bracing members extending between and rigidlysecured to said annular channels and said bar-like connections.

5. A tank of the construction set forth in claim 1, in which an axialcolumn-like support extends vertically between said outwardly convexedmembers and in which radial bracing members ex- 5 tend in asubstantially horizontal plane between each of said band-like connectingmembers and said column-like support.

6. A tank of the construction set forth in claim 1, in which theoutwardly convexed members intersect the cylindrical shell at an angleonly slightly in excess of ninety degrees.

7. In a storage tank, an upright substantially cylindrical sheet metalshell provided with relatively thicker top and bottom band-like portionshaving their side surfaces equally spaced from the side surfaces of thethinner portion, a continuous bar-like metal ring weld united to thedistal end of each band-like portion and extending at right anglesthereto, an annular Irustoconical member weld united to the inner edgeof each bar-like metal ring and a circular outwardly convexed sheetmetal member Of spherical section having its outer edge weld united tothe inner edge of each such annular frustoconical member.

8. A storage tank of the construction set forth in claim 7, in which acolumn-like support extends vertically between the centers of saidoutwardly convexed members, and radial beam-like members extend betweeneach band-like member and said column-like support,

9. A storage tank of the construction set forth in claim '7, in which acolumn-like support extends vertically between the centers of saidoutwardly convexed members, in which radial beamlike members extendbetween said band-like members and such column-like support and in whichannular beam-like members are positioned between such radial beam-likemembers and said so outwardly convexed members.

10. In a storage tank, an upright substantially cylindrical metal shell,relatively thicker bandlike members welded to the upper and lower edgesof such shell and having their side surfaces equally spaced from theside surfaces of the shell, a continuous bar-like metal ring welded tothe distal end of each band-like member and extending at right anglesthereto, an annular frusto-conical member having its outer edge weldedto the inner edge of each bar-like metal ring, a circular outwardlyconvexed member of spherical section welded to the inner edge of eachannular frusto-conical member, upper and lower groups of radiallyextending beam-like members, one group located immediately below theupper outwardly convexed member and the other immediately above thelower convexed member, means adjacent the vertical axis of the tank towhich the inner ends of the beamlike members of each group areconnected, and means connecting the outer ends of each group to theband-like members and to said bar-like metal rings.

11. A storage tank of the construction set forth in claim 10, in whichannular beam-like members are positioned between each group of radiallyextending beam-like members and the adjacent outwardly convexed member,and in which a column-like member extends vertically at the center ofthe tank and terminates within the means to which the inner ends of eachgroup of radially extending beam-like members is connected.

' JAMES O. JACKSON.

